In article , "jack" wrote:
I have a cabinet made of varnished plywood. I am adding oak molding and
then painting it all.

If you're going to paint it anyway, why bother with the expense of oak
molding? Pine, MDF, or plastic would work just fine.

Do I need to use a primer? If so, what kind?

Depends. Do you want the paint to stick?

I'd use an oil-based primer.

Do I have to sand the varnished plywood first?

It would sure help. Go to a real paint store (not the paint department at Home
Depot or Lowe's), tell them what you want to do, and ask them for
recommendations.